Historically, buildings were constructed out of natural resources that were readily and locally available, such as mud, wood, sod, or stone. These materials present a number of disadvantages, including relatively low structural integrity, the requirement of skilled artisans to assemble the materials, the lengthy amount of time involved in assembling the materials, and the need to independently insulate the building. Recently, builders developed updated building materials, including prefabricated building panels made of metal studs and foam insulation. The invention relates to improved methods of constructing prefabricated metal stud and foam panels.
One type of foam panel is made by kerfing a block of foam using a hot wire cutter. As shown in U.S. Pat. No. 6,167,624, issued to Lanahan et al., hot wire cutters are machines that heat tensioned wires measuring slightly longer than the length of the foam blocks to be cut. The foam block is secured in place while the superheated wire enters the foam block, cuts a trace of the outline of the stud, and exits the foam block. The result is a kerf that is approximately the same size and shape as the cross-section of the stud. Because hot wire cutters span and kerf the entire length of a foam block at once, they leave a slug that also spans the length of the foam block that must be removed prior to inserting the stud. The removal of the longitudinal slug must be performed manually, which constitutes a disadvantage to the use of hot wire cutters. It is an object of the invention to provide a process for constructing a foam panel that does not require manual removal of a longitudinal slug or manual installation of a stud.
Hot wire cutters also produce an inconsistent cut across the entire length of a foam block. Hot wire cutters are supposed to perform a straight cut, but because wires stretch when heated, hot wire cutters require a tensioning mechanism to maintain a straight wire. The tensioning mechanism must be very precise, as too much tension will break a hot wire, and too little tension will result in a bowed wire and resulting erroneous kerf. In typical industrial applications, wires are fragile and must be replaced several times a week. It is thus an object of the invention to provide a process for constructing a foam panel that improves upon the relative unreliability of hot wire cutters of the prior art.
As hot wires used in foam cutting break easily due to tension fluctuations, great care must be taken with respect to the type of foam used. Hot wire cutters of the prior art are preferred only in cutting pure, new foam blocks because impurities in recycled foam cause varied tension of the wires, often breaking them. Even new foam, such as expanded polystyrene (“EPS”), that consists of millions of tiny beads can break hot wire cutters if the size of the beads are not substantially uniform. Generally speaking, foam (particularly EPS) is not easily recyclable and is not biodegradable, and hot wire cutters do nothing to alleviate this general concern. Thus, it is another object of the invention to provide a process for constructing a foam panel that is capable of utilizing recycled and lower-grade foam.
Because foam panels are in relatively wide use, especially in construction of commercial buildings, many localities have specific building codes directed to foam panels. These types of regulations address thermal bridging, which means that the heat conductivity of metal studs may allow heat to be transmitted into or out of a building. A typical regulation requires at least 1.5 inches of foam between a metal stud and the exterior surface of the panel. That is, the metal stud must be embedded at least 1.5 inches into the foam, as measured from the exterior surface, to meet typical regulations. It is another object of the invention to produce a metal stud and foam panel combination capable of reliably meeting building regulations.
Traditional methods of constructing foam panels are not well suited to meet regulations for metal studded foam panels. Foam, and particularly EPS, is produced in rectangular blocks, and the curing process creates a natural curvature in these blocks. Traditional processes measure to a depth of 1.5 inches on each side of a foam block and kerf a line between these two points; however, the wire-cutting method does not result in a uniform depth because it does not contemplate the natural and inconsistent curvature inherent in most if not all foam blocks. It is thus another object of the invention to provide a foam panel having a uniform kerf depth along the entire length of the foam block, regardless of the natural curvature of the initial foam block component.
Compounding the problem of irregularly curved foam blocks is the fact that the wires used in hot wire cutters bow when they are heated. That is, the center of the wire dips as the wire expands during heating. As a result, kerfs made using a hot wire cutter are typically bowed as well, thus exacerbating the unreliability of foam blocks cut by longitudinal wires. It is another object of the invention to provide a foam panel having straight and uniform kerfs for the insertion of metal studs along the entire length of the foam block.
The inventors have experimented with various methods of solving these problems of the prior art. In one prototype designed to kerf a foam block for receiving a metal stud, the inventors utilized a circular saw to kerf a channel for the main beam of a metal stud, and used a separate hot wire knife to form the portion of the kerf corresponding to the channel and lip of the stud. The inventors never considered this implementation ready to patent due to several serious drawbacks that rendered the implementation unfit for industrial use. The first drawback was that the circular saw created tiny particles of foam that were easily ignited by the saw, the hot wire, or both. Foam burns rapidly and reaches high temperatures quickly when ignited, and even more seriously, melted foam sticks to human skin, clothing, and any other surface. The saw can compound problems resulting from burning foam by discharging melted, burning foam as the saw continues to cut. Therefore, this implementation presented a serious industrial safety issue. The second drawback was that a hot wire had to be welded to a stiffener to assist in keeping the resulting knife in the appropriate shape. However, the wire portion of the knife still melted frequently (albeit not as frequently as a hot wire cutter alone) due to thinness, and the difference in expansion of the two different metals throughout the operating range of the knife accelerated the knife's failure. Furthermore, since the knife was comprised of two separate metals, the knife was more expensive to produce for a relatively small gain in reliability over hot wire cutters of the prior art. The third drawback of this implementation is that there was no way to ensure uniform depth of the studs from the outer surface of the foam. Fourth, metal studs still had to be inserted into the machine by hand, as the saws and knives remained stationary while the foam block was moved through the machine. It is thus an object of the invention to provide a safe, reliable, consistent automated foam panel-making machine.